Anatomy of spinal cord

1. J E K A D E S H N A I D U P A N I R S E L V A M
F A C U L T Y O F M E D I C I N E , A I M S T
SPINAL CORD

2. INTRODUCTION
• Long cylindrical lowest part of central
nervous system. (45cm long in adults)
• Occupies upper 2/3 of vertebral canal and
gives rises to 31 pairs of spinal nerves.
• It extends from upper border of atlas
vertebra to the lower border of 1st lumbar or
upper border of 2nd lumbar vertebra.
• Superiorly it continues with medulla
oblongata and it terminates as conus
medullaris.
* The spinal cord is much shorter than
the length of vertebral column.

3. MENINGEAL COVERINGS
• Surrounded by 3 coverings;
• Dura mater (outermost )
• Arachnoid mater (middle)
• Pia mater (innermost)
• Space between dura mater and arachnoid mater is called as
subdural space
• Space between arachnoid mater and pia mater is called as
subarachnoid space – contains cerebrospinal fluid.

4. • Below the level conus medullaris,
only pia mater is continued as fibrous
cord – filum terminale.
• 20cm long and ends by getting attached
to the periosteum of dorsal surface of first
segment of coccyx.
• Dura and arachnoid mater along with
subarachnoid space containing
cerebrospinal fluid extend up to 2nd
sacral vertebra.
• Between lower border of L1 and S2
vertebrae, the subarachnoid space
contains spinal nerve roots which
constitute the cauda equina.
MENINGEAL COVERINGS

5. ENLARGEMENTS
• Cervical enlargement
• Extends from C4 to T2 spinal
segments with maximum
diameter at level of C6.
• Lumbar enlargement
• Extends from L2 to S3
segments. Maximum diameter
is at level S1.

6. CAUDAEQUINA
• Dorsal and ventral nerve
roots of right and left sides of
L2 to L5, S1 to S5 and Co1
nerves lie almost vertically
around filum terminale.

7. EXTERNALFEATURES
• Anteriorly
• Deep anterior median fissure – anterior spinal artery.
• Posteriorly
• Posterior median sulcus – a thin longitudinal groove from which a
septum runs in the depth of spinal cord.
• Each half is subdivided into:
• Anterior
• Lateral
• Posterior
• Ventral or motor nerve roots – anterolateral sulcus
• Dorsal or sensory nerve roots – posterolateral sulcus
Anterolateral and
posterolateral sulcus

8. INTERNALSTRUCTURE
• White matter – inside; grey
matter – outside.
• Central canal is found in the
centre of grey matter
• Grey matter is in the form of
“H”
• Grey matter comprises of one
posterior horn, one anterior
horn on each side
• * T1 to L1 and S2 to S4, there is
an additional lateral horn –
supplies the viscera.

9. SPINALNERVES
• Arise in pairs;
• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
• Each spinal nerve arises by a
series of dorsal and ventral
roots – unite in or near the
intervertebral foramen to
form spinal nerve.

10. DORSALROOTGANGLION
• Dorsal root has a ganglion made
up of pseudounipolar cells.
• With two processes
• Peripheral process is a dendrite.
• Central process is an axon.
• Joins with ventral root to form
spinal nerve.
• Spinal nerve divides into 2 rami;
• Dorsal ramus – supplies dorsal 1/3 of
the body wall but not the limbs
• Ventral ramus – supplies 2/3 of the
body wall including limbs.

11. SPINALSEGMENTS
• Part of spinal cord which a pair of dorsal nerve roots and
a pair of ventral nerve roots attached together.
• Length of spinal cord is smaller compared to vertebral
column, so the spinal segments do not correspond to the
vertebral level.

12. NUCLEI OFSPINALCORD
• Nuclei in Anterior grey horn
• Innervates the skeletal muscles
• The cells in anterior horn are arranged in 3 groups;
• Medial group – present throughout the entire extend of
spinal cord and innervates axial muscles
• Lateral group – present only in cervical and lumbar
enlargements and supplies muscles of limbs
• Central group – only in upper cervical segments as phrenic
nerve nucleus and nucleus of spinal roots of accessory
nerve.

13. • Nuclei in lateral horn
• Intermediolateral nucleus – acts as both afferent and efferent and seen
at T1 to L2 and S2 to S4 segments
• Intermediomedial nucleus
• Nuclei in posterior horn
• Posteromarginal nucleus – thin layer of neurons caps posterior horn
• Substantia gelatinosa – found at tip of posterior horn. Acts as relay
station for pain and temperature fibres
• Nucleus proprius – lies subjacent to sustantia gelatinosa
• Nucleus dorsalis – relay nuclear for reflex and unconcsious
proprioceptive impulses to the cerebellum.
NUCLEI OFSPINALCORD

14. LAMINAR
• Also known as laminae of Rexed
• Ten layers of neurons
• Numbered consecutively starting from tip of dorsal horn and
moving ventrally into ventral horn.
• Lamina I – IV corresponds to dorsal horn head.
• Lamina V corresponds to neck.
• Lamina VI corresponds to base of dorsal horn.
• Lamina VII- corresponds to intermediate area.
• Lamina VIII & IX occupies the ventral horn
• Lamina X is the grey matter surrounding the central canal.

15. TRACTSOFSPINALCORD
• Collection of nerve fibres that connect to masses of
grey matter within central nervous system.
• Tract is a collection of nerve fibres having the same
origin, course and termination.
• Tracts may be ascending or descending.
• Tracts are named after the masses of grey matter
connected by them. E.g. – corticospinal
tract,spinothalamic tract.
• Tracts are sometimes referred to as fasciculi or
leminisci .

16. DESCENDINGTRACTS
• The pyramidal or corticospinal tract descends from
cerebral cortex to the spinal cord
1. Lateral corticospinal tract – lies in lateral funiculus
2. Anterior corticospinal tract – lies in anterior funiculus
• Extrapyramidal tracts are;
1. Rubrospinal tract
2. Medial reticulospinal tract
3. Lateral reticulospinal tract
4. Olivospinal tract
5. Vestibulospinal tract
6. Tectospinal tract

19. PYRAMIDALTRACT
• Originates in the motor cortex.
• Pass through genu of the internal
capsule, crus cerebri, pons,
pyramids of medulla.
• Decussates and descends in the
lateral column of the spinal cord-
lateral cortricospinal tract.
• 10% does not cross and descends
in the anterior column of the spinal
cord and form anterior
corticospinal tract.
• They relay in the anterior horn cells
of the spinal cord.
• These anterior horn cells project
directly to muscle and control
muscular contraction.

20. • Fibres originate in the region of
sensorimotor cortex.
• Pass through posterior limb of
internal capsule & middle portion
of crus cerebri to the cranial
nerve nuclei in the brain stem.
• Projects through cranial nerves to
areas of supply for motor
functions
CORTICOBULBARTRACT

21. EXTRAPYRAMIDALTRACTS
Vestibulospinal tract
• Lateral vestibulospinal – arise from lateral vestibular nucleus
in the brain stem and course downward, uncrossed, in the
anterior funiculus of the spinal cord.
• Medial vestibulospinal – arise from medial vestibular nucleus
in the brain stem and descend within the cervical spinal
cord,with both crossed & uncrossed, in the anterior funiculus
of the spinal cord to terminate at cervical levels.
• Function - provide excitatory input to extensor muscles.

22. EXTRAPYRAMIDALTRACTS
Rubrospinal tract
• Arises from the red nucleus of midbrain.
• Cross in the midbrain and descends in the pons, medulla and
in the lateral column of the spinal cord.
• Synapses in the ventral horn interneurons of the spinal cord.
• Controls motor tone.

23. EXTRAPYRAMIDALTRACTS
Reticulospinal tract
• Arises in the reticular formation of the brain stem.
• Descends in both the ventral and lateral white columns.
• Both crossed and uncrossed descending fibres are present.
• Terminate on dorsal grey column neurons may modify
transmission of sensation of body - pain.

24. EXTRAPYRAMIDALTRACTS
Tectospinal tract
• Arises from superior colliculus of the midbrain.
• Decussates & passes through contralateral anterior white
column.
• Relay in ventral grey interneurons.
• Function causes sudden movement of head in response to
visual or auditory stimuli.

25. DESCENDINGTRACT
Tracts Origin Functions
Corticospinal
Lateral & anterior
Motor cortex of
cerebrum
Controls voluntary
movements
Rubrospinal Red nucleus of
midbrain
Facilitatory influence
of flexor tone
Reticulospinal
Medial & Lateral
Reticular formation voluntary
movements and
muscle tone
Tectospinal Superior colliculus Spinovisual reflexes
Vestibulospinal
Medial & Lateral
Lateral vestibular
nucleus
Controls body
equilibrium
Olivospinal Inferior olivary
nucleus
Controls motor tone

26. ASCENDINGTRACT
• Ascending tracts are seen in spinal cord & brain
stem.
• They are multineuronal pathways by which afferent
impulses arising from various parts of the body are
conveyed to different parts of the brain.
• Usually three set of neurons:
- First order neurons
- Second order neurons
- Third order neurons.

27. FIRSTORDER NEURON
• Each neuron in dorsal root ganglion gives off a
peripheral process & a central process.
• The peripheral processes of the neurons form the
afferent fibres of peripheral nerves. They end in
relation to sensory end organs situated in various
tissues.
• The central processes of these neurons enter the
spinal cord through the dorsal nerve roots.

28. SECONDORDERNEURON
• Having entered the spinal cord the central processes
as a rule, terminate by synapsing with cells in spinal
grey matter.
• Some of them may run upwards in the white matter
of the cord to form ascending tracts.
• The majority of ascending tracts are however formed
by axons of cells in spinal grey matter.

29. THIRDORDER NEURON
• In the case of pathways that convey sensory
information to the cerebral cortex the second order
neurons end by synapsing with neurons in the
thalamus.
• Third order sensory neurons located in the thalamus
carry the sensations to the cerebral cortex.

30. SPINOTHALAMICTRACTS
• Anterior spinothalamic
tract- ascend in the anterior
funiculus and ascend to the
medulla.
• Merges with the medial
lemniscus.
• End ultimately in the
thalamus.
• Fibres of lateral
spinothalamic tract enter
the lateral funiculus.
• Ascend through medulla,
pons and midbrain (spinal
lemniscus)
• End in the thalamus (VPL
nucleus).
Anterior spinothalamic Lateral spinothalamic

31. ANTERIORSPINOTHALAMIC

32. LATERALSPINOTHALAMIC

33. SPINORETICULARTRACT
• Begin from the spinal neurons mainly in lamina VII.
• Fibres are partly crossed & partly uncrossed.
• Fibres ascend in the ventrolateral part of the spinal
cord, intermingling with spinothalamic tracts.
• They end in the reticular formation of the medulla &
pons.
• Probably carries the pain.

34. SPINO-OLIVARYTRACT
• Is also a crossed tract.
• It lies at the junction of the anterior & lateral funiculi
of the spinal cord.
• The fibres of the tract end in accessory olivary nuclei.
• May carry exteroceptive impulses.

35. FUNCTIONSOF ASCENDINGTRACT
• Anterior
spinothalamic –Simple
touch and pressure.
• Lateral spinothalamic
– Pain & temperature
• Fasciculus gracilis &
Fasciculus cuneatus -
Proprioceptiive
impulses,vibration
sense, fine touch, tactile
localization &
discrimination
• Anterior spinocerebellar -
Proprioceptive impulses.
• Posterior spinocerebellar
-Proprioceptive impulses.
• Spinotectal & spino
olivary - Spinovisual
reflexes.
• Dorsolateral tract -pain &
temperature

37. ARTERIALSUPPLY
• The spinal cord receives its arterial
supply from three small arteries.
• Two posterior spinal arteries and one
anterior spinal artery.
• These longitudinally running arteries are
reinforced by small segmental arteries
that arise from arteries outside the
vertebral column and enter the vertebral
canal through the intervertebral
foramina.
• Anterior and posterior spinal arteries
anastomose on the surface of the cord
and send branches into the substance of
the white and grey matter.

38. ARTERIALSUPPLY
Anterior spinal artery:
•The anterior spinal artery is formed by
the union of two arteries, each of which
arises from the vertebral artery inside
the skull.
•The anterior spinal artery then
descends on the anterior surface of the
spinal cord within the anterior median
fissure.
•Branches from the anterior spinal
artery supply the anterior two-thirds of
the spinal cord.

39. Posterior spinal arteries:
• The posterior spinal arteries arise either directly from the
vertebral arteries inside the skull or indirectly from the
posterior inferior cerebellar arteries.
• They descend on the posterior surface of the spinal cord close
to the posterior nerve roots and gives off branches that enter
the substance of the cord.
• The posterior spinal arteries supply the posterior one-third of
the spinal cord.
ARTERIALSUPPLY

40. ARTERIALSUPPLY
Segmental spinal arteries:
• At each intervertebral foramen, posterior and anterior
spinal arteries are reinforced by small segmental
arteries on both sides.
• The arteries are branches of deep cervical, intercostal,
and lumbar arteries.
• Segmental artery enters the vertebral canal, gives rise
to anterior and posterior radicular arteries that
accompany the anterior and posterior nerve roots to
the spinal cord.
• Additional feeder arteries enter the vertebral canal.
One large feeder artery, the great anterior medullary
artery of Adamkiewicz, arises from the aorta a major
source of blood to the lower two-thirds of the spinal
cord.

41. VENOUS DRAINAGE
• 6 longitudinal spinal veins.
• They communicate superiorly within the
skull with the veins of the brain and the
venous sinuses and drain through
intervertebral foramina into:
- Vertebral veins in the neck.
- Azygos vein in the thorax.
- Lumbar veins in the lumbar
region.
- Lateral sacral veins in the sacral
region.

42. CLINICALASPECTS

43. LUMBAR PUNCTURE
Lumbar puncture:
 Obtaining the CSF from the lumbar cistern for
diagnostic purposes.
 Done between L3 and L4 vertebrae
Layers that the spinal needle traverse are:
1. Skin
2. Superficial fascia
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space containing the internal vertebral venous
plexus
7. Dura mater
8. Arachnoid mater.

44. EPIDURALANAESTHESIA
• Epidural space - space
between the dura and the
periosteum, especially larger
at the level of S2 vertebra.
• Local anaesthetic can be
injected, epidural
anaesthesia.

45. SPINABIFIDAOCCULTA
• Congenital absence of
spinous process and
lamina.
• No visible meninges or
neural tissue.
• Often incidental finding

46. SPINABIFIDACYSTICA
Meningocele :
• Congenital defect in
vertebral arches with
cystic distension of
meninges.
• No abnormality of neural
tissue.

47. SPINABIFIDACYSTICA
Meningomyelocele:
• Congenital defect in
vertebral arches with
cystic distension of
meninges.
• With structural or
functional
abnormality of spinal
cord or cauda equina.